The sirtuins are a family of NAD+-dependent deacylases that regulate metabolism and maintain metabolic homeostasis by removing chemical modifications from lysine residues of key metabolic enzymes. SIRT5 is located in the mitochondria and uniquely removes succinyl modifications from lysine residues. Recently a number of metabolic enzymes have been identified as regulated by SIRT5 mediated desuccinylation. However, the physiological significance of SIRT5 remains unknown. The long-term goal of this work is to better understand the crosstalk between cardiac function and metabolism and to ultimately identify novel therapeutic interventions to treat people with heart diseases. The objective of this research proposal is to characterize the effect of SIRT5 on cardiac function under basal and stressed conditions, and to identify specific proteins that are regulated by SIRT5. Based on preliminary data, the hypothesis guiding this work is that SIRT5 mediated desuccinylation regulates key pathways of oxidative metabolism and impaired SIRT5 function leads to metabolic inflexibility that affects cardiac function. The rationale for the proposed research is that the physiological role of SIRT5 is currently unknown, and identifying an effect of SIRT5 on cardiac function will establish a physiological role for SIRT5 via the mechanism of SIRT5 mediated desuccinylation. Guided by the preliminary data, the hypothesis will be tested by the following specific aims: 1) characterize the effect of SIRT5 on cardiac function; and 2) identify a mechanism by which SIRT5 regulates cardiac metabolism. In the first aim, heart function will be characterized in a SIRT5 knockout mouse under basal and stressed conditions using techniques of echocardiogram, pressure volume loop analysis, and histology. In the second aim, a specific enzyme will be identified and validated as a target of SIRT5 mediated desuccinylation using established biochemical assays. Based on preliminary data and the well-developed research design, this proposal holds a strong likelihood of scientific success. Further, the applicant has a high training potential based on a unique combination of classic scientific training in biochemistry coupled with current techniques in animal physiology and cardiac function research. The proposed research is significant because it is expected to lead to the identification of a physiological role for SIRT5 in regulating cardiac function and the identification of a metabolic mechanism for this role. Ultimately, this understanding will lead to deeper knowledge of cardiac metabolism and its relation to heart diseases in order to realize improved therapies for heart diseases.